1. Field of the Invention
Rusting of critical engine parts causes premature engine trouble and shortens engine life. The role of the lubricating oil as the primary deterrent to engine rusting is widely recognized. The increasing oil drain intervals recommended by car manufacturers increase the importance of having effective rust inhibitors present in automotive lubricating oils. Since oils with high alkalinity prevent corrosion, alkaline agents such as overbased calcium and barium salts of organic sulfonates are useful rust inhibitors. However, these additives contribute to the ash of the oil. In order to provide an effective rust inhibitor in automotive lubricating oils while reducing the ash content of the oil, efforts have been made to find improved rust inhibiting compositions.
2. Description of the Prior Art
Such compositions for preventing the corrosion of metals have been described previously. For example, U.S. Pat. No. 2,739,126 discloses an anti-corrosive composition which contains a polyvalent metal sulfonate and an oil-soluble glycol. U.S. Pat. No. 2,785,078 discloses aliphatic diamines as corrosion inhibiting additives in compositions which include petroleum oils.
Fuel compositions which include calcium overbased calcium sulfonates are disclosed in U.S. Pat. Nos. 3,539,312 and 3,707,360. These compositions are described therein as being useful as smoke suppressants.
U.S. Pat. No. 3,969,235 discloses succinimides prepared from polybutene-P.sub.2 S.sub.5 and an alkenylsuccinic anhydride as components of lubricating oil compositions.
A mixture of fatty material consisting essentially of dimers and trimers of ethylenic fatty acids and of a phenolic compound is disclosed as an additive for fuel compositions in U.S. Pat. No. 3,346,355.